[Akonadi] [Bug 328286] New: Broken logic in DataStore::setItemFlags causes flags to be erroneously removed

[Tomas Trnka]

https://bugs.kde.org/show_bug.cgi?id=328286

            Bug ID: 328286
           Summary: Broken logic in DataStore::setItemFlags causes flags
                    to be erroneously removed
    Classification: Unclassified
           Product: Akonadi
           Version: 1.10.3
          Platform: unspecified
                OS: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: NOR
         Component: server
          Assignee: kdepim-bugs at kde.org
          Reporter: tomastrnka at gmx.com

User-visible problem: Ignoring threads in KMail doesn't work properly, some
messages get spuriously un-ignored on next sync.

Findings:
- Even though the messages get the $IGNORED flag set correctly in DB, they
don't have it on the IMAP server.
- IMAP communication trace shows that for the affected messages, two commands
are submitted:
STORE +FLAGS ($IGNORED)
STORE -FLAGS ($IGNORED)
This is the result of ChangeItemsFlagsTask getting run with addedFlags and
removedFlags both containing $IGNORED.

Root cause (found using GDB on the imap resource and server, following the
notification flow):
DataStore::setItemsFlags doesn't properly handle setting a flag that is already
set. 
Calling it with flags = $IGNORED makes it delete and re-add the $IGNORED flag
in the DB (which is harmless) and emit itemsFlagsChanged with both addedFlags
and removedFlags containing $IGNORED.

Quick hacky fix:
Before emitting the notification, remove flags that are both in addedFlags and
removedFlags from removedFlags.

However, I see a problem here in need of discussion:
The way DataStore::setItemsFlags handles the DB isn't optimal either - why
delete and re-insert the flag that's already there? It would possibly be better
to just delete the flags that are getting removed and insert the new ones, thus
doing nothing if nothing needs to be done.
However, this was basically the state before commit
http://quickgit.kde.org/?p=akonadi.git&a=commit&h=ee8b3d209553351c338cf5b069a2c0bda0e25298
, so I'm wondering if that's a good idea.

Reproducible: Always

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